U.S. patent application number 13/636256 was filed with the patent office on 2013-03-07 for radio base station apparatus and transmission power control method.
This patent application is currently assigned to NTT DOCOMO, INC.. The applicant listed for this patent is Teruo Kawamura, Yoshihisa Kishiyama, Daisuke Nishikawa. Invention is credited to Teruo Kawamura, Yoshihisa Kishiyama, Daisuke Nishikawa.
Application Number | 20130058293 13/636256 |
Document ID | / |
Family ID | 44762652 |
Filed Date | 2013-03-07 |
United States Patent
Application |
20130058293 |
Kind Code |
A1 |
Nishikawa; Daisuke ; et
al. |
March 7, 2013 |
RADIO BASE STATION APPARATUS AND TRANSMISSION POWER CONTROL
METHOD
Abstract
The present invention provides a radio base station apparatus
and a transmission power control method that do not deteriorate the
uplink reception quality of cell-edge users when uplink MU-MIMO
transmission is applied. The transmission power control method of
the present invention includes the steps of: in a radio base
station apparatus that performs space division multiplexing between
users by uplink MU-MIMO transmission: controlling transmission
power according to a number of MU-MIMO multiplexed users; and
transmitting transmission power information to match the number of
MU-MIMO multiplexed users; and in a mobile terminal apparatus:
setting transmission power using the transmission power
information; and transmitting an uplink signal by the transmission
power.
Inventors: |
Nishikawa; Daisuke; (Tokyo,
JP) ; Kishiyama; Yoshihisa; (Tokyo, JP) ;
Kawamura; Teruo; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nishikawa; Daisuke
Kishiyama; Yoshihisa
Kawamura; Teruo |
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP |
|
|
Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
44762652 |
Appl. No.: |
13/636256 |
Filed: |
March 30, 2011 |
PCT Filed: |
March 30, 2011 |
PCT NO: |
PCT/JP2011/057965 |
371 Date: |
November 16, 2012 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 52/58 20130101;
H04W 52/146 20130101; H04W 52/42 20130101; H04W 52/242 20130101;
H04W 52/248 20130101; H04W 52/08 20130101; H04W 52/346 20130101;
H04W 52/243 20130101; H04B 7/0452 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 52/34 20090101
H04W052/34; H04W 52/14 20090101 H04W052/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2010 |
JP |
2010-087266 |
Claims
1. A radio base station apparatus that performs space division
multiplexing between users by uplink MU-MIMO transmission, the
radio base station apparatus comprising: a transmission power
control section configured to control transmission power according
to a number of MU-MIMO multiplexed users; and a transmission
section configured to transmit transmission power information to
match the number of MU-MIMO multiplexed users.
2. The radio base station apparatus as defined in claim 1, wherein
the transmission power control section comprises: a format
selection section configured to select a transmission power control
command format; and a command determining section configured to
determine a transmission power control command in the selected
transmission power control command format.
3. The radio base station apparatus as defined in claim 2, wherein
the transmission section transmits the transmission power control
command format and the transmission power control command as the
transmission power information.
4. The radio base station apparatus as defined claim 1, wherein the
transmission power control section performs fractional transmission
power control based on an equation including a surrounding-cell
interference fluctuation correction term that varies with the
number of MU-MIMO multiplexed users.
5. The radio base station apparatus as defined in claim 4, wherein
the surrounding-cell interference fluctuation correction term
includes an attenuation coefficient that adjusts a surrounding-cell
interference reduction amount.
6. The radio base station apparatus as defined in claim 5, wherein
the transmission section transmits the number of MU-MIMO
multiplexed users and the attenuation coefficient as the
transmission power information.
7. A transmission power control method comprising the steps of: in
a radio base station apparatus that performs space division
multiplexing between users by uplink MU-MIMO transmission:
controlling transmission power according to a number of MU-MIMO
multiplexed users; and transmitting transmission power information
to match the number of MU-MIMO multiplexed users; and in a mobile
terminal apparatus: setting transmission power using the
transmission power information; and transmitting an uplink signal
by the transmission power.
8. The transmission power control method as defined in claim 7,
further comprising the steps of: in the radio base station
apparatus: selecting a transmission power control command format;
and determining a transmission power control command in the
selected transmission power control command format.
9. The transmission power control method as defined in claim 8,
wherein the transmission power information is the transmission
power control command format and the transmission power control
command.
10. The transmission power control method as defined in claim 7,
further comprising the step of: in the radio base station
apparatus: performing fractional transmission power control based
on an equation including a surrounding-cell interference
fluctuation correction term that varies with the number of MU-MIMO
multiplexed users.
11. The transmission power control method as defined in claim 10,
wherein the surrounding-cell interference fluctuation correction
term includes an attenuation coefficient that adjusts a
surrounding-cell interference reduction amount.
12. The transmission power control method as defined in claim 11,
wherein the transmission power information is the number of MU-MIMO
multiplexed users and the attenuation coefficient.
Description
TECHNICAL FIELD
[0001] The present invention relates to a radio base station
apparatus and a transmission power control method to control
transmission power when uplink MU-MIMO (Multi-User Multi-Input
Multi-Output) is applied.
BACKGROUND ART
[0002] In the LTE (Long Term Evolution) system defined in 3GPP (3rd
Generation Partnership Project), SC-FDMA (Single-Carrier Frequency
Division Multiple Access) is employed on the uplink, which realizes
a low peak-to-average power ratio (PAPR) and which is effective to
increase coverage. Consequently, by means of scheduling at a radio
base station apparatus (BS: Base Station), basically, radio
resources of a certain frequency and time are allocated to one
mobile terminal apparatus (UE: User Equipment), and therefore the
users in the same cell are orthogonal to each other in the
frequency and time domains. However, the LTE system is based on
one-cell frequency repetition, and therefore there is significant
interference from the surrounding cells, and, in particular, the
interference level from UEs located at cell edges is high.
Consequently, to compensate for such surrounding-cell interference
and maintain certain reception quality, a measure against
inter-cell interference becomes necessary.
[0003] Uplink transmission power control plays a significant role
as a measure against inter-cell interference, and a radio base
station apparatus is demanded to control the transmission power of
a mobile terminal apparatus, to satisfy required reception quality,
by taking into account the propagation loss between the user and
the radio base station apparatus and the interference against the
surrounding cells. In the LTE system, fractional transmission power
control is employed as a transmission power control method to take
inter-cell interference into account.
[0004] Signals to transmit on the uplink of the LTE system (PUSC
(Physical Uplink Shared Channel), PUCCH (Physical Uplink Control
Channel), SRS (Sounding Reference Signal) and so on) become desired
signals if a mobile terminal apparatus is under a cell (for
example, the signal from UE 1 to BS 1 and the signal from UE 2 to
BS 2 in FIG. 1), but become interference signals if the mobile
terminal apparatus is not under a cell (for example, the signal
from UE 1 to BS 2 and the signal from UE 2 to BS1 in FIG. 1).
[0005] The transmission power of such uplink signals is controlled
by the combination of open loop control, which is based on
parameters reported from a radio base station apparatus in a
comparatively long cycle and the propagation loss measured by the
mobile terminal apparatus, and closed loop control, which is based
on TPC commands reported from a radio base station apparatus in a
comparatively short cycle based on the situation of communication
between the radio base station apparatus and a mobile terminal
apparatus (for example, the received SINR (Signal to Interference
plus Noise Ratio) at the radio base station apparatus). To be more
specific, the transmission power of the PUSCH is given by following
equation 1 (non-patent literature 1).
P.sub.PUSCH(i)=min{P.sub.MAX,10
log.sub.10(M.sub.PUSCH(i))+P.sub.0.sub.--.sub.PUSCH(j)+.alpha.PL+.DELTA..-
sub.TF(i)+f(i)} (Equation 1)
[0006] This fractional transmission power control can reduce
inter-cell interference by setting the target received power
according to the propagation loss PL of a mobile terminal apparatus
(which is realized by the open loop control parameter .alpha.).
[0007] FIG. 2 is a diagram for explaining fractional transmission
power control. In FIG. 2, the vertical axis represents the target
received power (P.sub.O.sub.--PUSCH), and the horizontal axis
represents propagation loss (PL). Fractional transmission power
control is designed to make the target received power of mobile
terminal apparatuses that are present at cell edges lower, for the
purpose of suppressing inter-cell interference. That is to say,
when the propagation loss (PL) is high, it is likely that the user
is present at a cell edge, and, when the propagation loss is low,
it is likely that the user is present near a radio base station
apparatus, so that the target received power of a mobile terminal
apparatus of a user near a radio base station apparatus is made
relatively high, and the target received power of a mobile terminal
apparatus of a user at a cell edge is made relatively low. The
inclination of the primary characteristic line to show such
relationship is -(1-.alpha.).
[0008] Meanwhile, in the LTE system, as a technique to increase the
capacity of the uplink, MU-MIMO transmission is drawing attention
and expectation. MU-MIMO transmission is a technique of improving
the spectral efficiency dramatically by multiplexing signals of a
plurality of users in frequency/time. In this case, too, desired
signals are provided if a mobile terminal apparatus is under a cell
(for example, the signal from UE 1 or UE 4 to BS 1 and the signal
from UE 2 or UE 3 to BS 2 in FIG. 3), but, if the mobile terminal
apparatus is not under a cell, interference signals are provided
(for example, the signal from UE 1 or UE 4 to BS 2 and the signal
from UE 2 or UE 3 to BS 1 in FIG. 1).
CITATION LIST
Non-Patent Literature
[0009] Non-Patent Literature 1: 3GPP, TS36.213, V8.7.0, "Evolved
Universal Terrestrial Radio Access (E-UTRA); Physical layer
procedures"
SUMMARY OF INVENTION
Technical Problem
[0010] For the purpose of maximizing capacity, generally, a radio
base station apparatus performs frequency scheduling (in minimum 1
RB (Resource Block) units) based on the uplink reception quality of
each user, as shown in FIG. 4, and selects, adaptively, the
combination of users to multiplex when MU-MIMO transmission is
applied. This frequency scheduling is performed in minimum 1-TTI
(Transmission Time Interval) cycle. Consequently, when MU-MIMO
transmission is applied, it may happen that the number of users to
multiplex varies per 1 RB and 1 TTI.
[0011] In conventional fractional transmission power control, fixed
transmission power is set regardless of the number of MU-MIMO
multiplexed users. Consequently, in the event MU-MIMO transmission
is applied, as shown in FIG. 5, differences are produced in the
received power at a radio base station apparatus, per 1 RB and 1
TTI. When differences are produced in the received power at a radio
base station apparatus, for example, the problem of increased
surrounding-cell interference, and the problem of producing
significant fluctuation of surrounding-cell interference over time
in adaptive resource control based on interference information
prior to control delay, are raised. These problems in particular
deteriorate the uplink reception quality of cell-edge users and
damage the coverage.
[0012] The present invention is made in view of above problems, and
it is therefore an object of the present invention to provide a
radio base station apparatus and a transmission power control
method that do not deteriorate the uplink reception quality of
cell-edge users when uplink MU-MIMO transmission is applied.
Solution to Problem
[0013] A radio base station apparatus of the present invention
performs space division multiplexing between users by uplink
MU-MIMO transmission, and includes: a transmission power control
section that controls transmission power according to a number of
MU-MIMO multiplexed users; and a transmission section that
transmits transmission power information to match the number of
MU-MIMO multiplexed users.
[0014] A transmission power control method of the present invention
includes the steps of: in a radio base station apparatus that
performs space division multiplexing between users by uplink
MU-MIMO transmission: controlling transmission power according to a
number of MU-MIMO multiplexed users; and transmitting transmission
power information to match the number of MU-MIMO multiplexed users;
and in a mobile terminal apparatus: setting transmission power
using the transmission power information; and transmitting an
uplink signal by the transmission power.
Advantageous Effects of Invention
[0015] According to the transmission power control of the present
invention, transmission power is controlled according to the number
of MU-MIMO multiplexed users and transmission power information to
match that number of MU-MIMO multiplexed users is transmitted, so
that the uplink reception quality of cell-edge users is not
deteriorated when uplink MU-MIMO transmission is applied.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a diagram for explaining the uplink in the LTE
system;
[0017] FIG. 2 is a diagram for explaining fractional transmission
power control;
[0018] FIG. 3 is a diagram for explaining MU-MIMO transmission;
[0019] FIG. 4 is a diagram for explaining the selection of
combinations of users to multiplex when MU-MIMO transmission is
applied;
[0020] FIG. 5 is a diagram for explaining a problem with fractional
transmission power control when MU-MIMO transmission is
applied;
[0021] FIG. 6 is a diagram showing an example of TPC command format
to use in the transmission power control the first method according
to the present invention;
[0022] FIG. 7 is a flowchart for explaining the transmission power
control of the first method according to the present invention;
[0023] FIG. 8 is a diagram for explaining the transmission power
control of the second method according to the present
invention;
[0024] FIG. 9 is a diagram for explaining the transmission power
control of the second method;
[0025] FIG. 10 is a diagram showing a configuration of a radio
communication system having a radio base station apparatus and a
mobile terminal apparatus according to an embodiment of the present
invention;
[0026] FIG. 11 is a block diagram showing a schematic configuration
of a radio base station apparatus according to an embodiment of the
present invention;
[0027] FIG. 12 is a block diagram showing a configuration of a
baseband signal processing section in the radio base station
apparatus shown in FIG. 11;
[0028] FIG. 13 is a block diagram showing a configuration of a
transmission power control section according to embodiment 1, in
the baseband signal processing section shown in FIG. 12;
[0029] FIG. 14 is a block diagram showing a schematic configuration
of a mobile terminal apparatus according to an embodiment of the
present invention;
[0030] FIG. 15 is a block diagram showing a configuration of a
baseband signal processing section according to embodiment 1, in
the mobile terminal apparatus shown in FIG. 14;
[0031] FIG. 16 is a block diagram showing a configuration of a
transmission power control section according to embodiment 2, in
the baseband signal processing section shown in FIG. 12; and
[0032] FIG. 17 is a block diagram showing a configuration of a
baseband signal processing section according to embodiment 2, in
the mobile terminal apparatus shown in FIG. 14.
DESCRIPTION OF EMBODIMENTS
[0033] Now, embodiments of the present invention will be described
below in detail with reference to the accompanying drawings. The
present invention has a feature of controlling transmission power
according to the number of MU-MIMO multiplexed users, in fractional
transmission power control. That is to say, in the event uplink
MU-MIMO transmission is applied, if fractional transmission power
control is executed without considering the number of MU-MIMO
multiplexed users, as shown in FIG. 5, the fluctuation of received
power at a radio base station apparatus per 1 RB and 1 TTI becomes
greater. Consequently, the surrounding-cell interference increases,
and, by this means, in adaptive resource control, significant
fluctuation of surrounding-cell interference over time is produced.
Consequently, with the present invention, by performing fractional
transmission power control taking into account the number of
MU-MIMO multiplexed users, the fluctuation of received power at a
radio base station apparatus per 1 RB and 1 TTI is reduced, the
surrounding-cell interference is prevented from increasing, and the
surrounding-cell interference is prevented from fluctuating
significantly over time in adaptive resource control. As a result
of this, it is possible to secure coverage without deteriorating
the uplink reception quality of cell-edge users.
[0034] So, for the method of reducing the fluctuation of received
power at a radio base station apparatus per 1 RB and 1 TTI, the
present invention proposes two methods. The first method is a
method of performing transmission power control upon MU-MIMO
transmission by expanding the number of TPC command bits and using
TPC commands of an expanded number of bits. Also, the second method
is a method of performing fractional transmission power control by
adding a term related to the number of MU-MIMO multiplexed users to
the equation of fractional transmission power control (equation 1),
and performing fractional transmission power control based on the
resulting equation.
[0035] In the first method, transmission power control upon MU-MIMO
transmission is realized by expanding the number of TPC command
bits, which is reported from a radio base station apparatus to a
mobile terminal apparatus individually through L1/L2 signaling (UL
grant) via the PDCCH, and expanding the range of transmission power
control. For example, as shown in FIG. 6, the DCI (Downlink Control
Information) format X of the PDCCH (Physical Downlink Control
Channel) of an expanded number of bits (3 bits here) is used. The
selected DCI format X is reported from the radio base station
apparatus to the mobile terminal apparatus through higher layer
signaling.
[0036] There are two types of TPC commands, namely "Accumulate" and
"Absolute," each using the format X of an expanded number of bits.
Here, in the case of "Accumulate," the TPC command to transmit is
set according to "the fluctuation of the number of UEs to
multiplex," and, in the event of "Absolute," the TPC command is set
according to "the number of UEs to multiplex." For example, in the
event the number of MU-MIMO multiplexed users N.sub.UE changes from
1 to 2, the TPC command=-3 dB is selected. Note that which one of
"Accumulate" and "Absolute" is used for the TPC command, is
notified from the radio base station apparatus to the mobile
terminal apparatus through higher layer signaling. According to
this first method, the parameters are not increased, so that it is
possible to prevent the amount of signaling from increasing.
[0037] FIG. 7 is a flowchart for explaining the transmission power
control of the first method according to the present invention.
First, the radio base station apparatus (BS) selects the TPC
command format (proposed format), and reports the selected TPC
command format to a mobile terminal apparatus (UE) to which MU-MIMO
transmission is anticipated to be applied, through higher layer
signaling. Then, whether the TPC command is the Accumulate-type or
the Absolute-type is also reported (ST11). Following this, the
radio base station apparatus performs scheduling adaptively in TTI
units, determines the TPC command in the selected TPC command
format, and reports the TPC command to the mobile terminal
apparatus to be scheduled, by L1/L2 signaling (ST12). In this case,
the transmission power information is the TPC command format and
TPC command.
[0038] By this means, whether the TPC command is the
Accumulate-type or the TPC command is the Absolute-type, is
reported to the mobile terminal apparatus (ST13). When it is
reported that the TPC command is the Accumulate-type, a TPC command
to match the number of fluctuating MU-MIMO multiplexing is reported
from the mobile terminal apparatus to the radio base station
apparatus (ST14). On the other hand, when it is reported that the
TPC command is the Absolute-type, a TPC command to match the number
of MU-MIMO multiplexing is reported from the radio base station
apparatus (ST15). The mobile terminal apparatus sets transmission
power according to the reported TPC command (ST16), and performs
uplink data transmission by the set transmission power (ST17).
[0039] According to the second method, a term that relates to the
number of MU-MIMO multiplexed users N.sub.UE (a surrounding-cell
interference fluctuation correction term, which varies with the
number of MU-MIMO multiplexed users) is added to the equation of
fractional transmission power control (equation 1), and fractional
transmission power control is performed based on that equation
(following equation 2).
P.sub.PUSCH(i)min{P.sub.MAX,10
log.sub.10(M.sub.PUSCH(i))+P.sub.0.sub.--.sub.PUSCH(j)+.alpha.PL+.DELTA..-
sub.TF(i)+f(i)-.beta.10 log.sub.10N.sub.UE} (Equation 2)
[0040] In this way, by providing the term of .beta.10 log
10N.sub.UE, it is possible to reduce the fluctuation of received
power at the radio base station apparatus per 1 RB and 1 TTI, and
prevent the surrounding-cell interference from fluctuating
significantly in adaptive resource control. As a result of this, it
is possible to secure coverage without deteriorating the uplink
reception quality of cell-edge users.
[0041] The surrounding-cell interference reduction amount can be
adjusted by means of an attenuation coefficient
.beta.(0.ltoreq..beta..ltoreq.1) for adjusting the surrounding-cell
interference reduction amount, which is included in the
surrounding-cell interference fluctuation correction term. When
.beta.=0 holds, normal fractional transmission power control is
performed (equation 1). When .beta.=1 holds, as shown in FIG. 8, it
is possible to make the reception level constant regardless of the
number of MU-MIMO multiplexing. When .beta.=1 is set, it is
possible to reduce the fluctuation of surrounding-cell interference
without increasing the amount of surrounding-cell interference
regardless of the number of MU-MIMO multiplexing. In particular,
there is an effect of reducing the deterioration of cell-edge user
throughput (coverage). On the other hand, when .beta.=1 holds, the
effect of increasing the MU-MIMO transmission capacity is
suppressed. Consequently, it is preferable to adequately set the
attenuation coefficient .beta., taking into account the
relationship between capacity and coverage
(0.ltoreq..beta..ltoreq.1).
[0042] The radio base station apparatus broadcasts the value of the
attenuation coefficient .beta. via, for example, the PBCH (Physical
Broadcast Channel), or reports individually, through higher layer
signaling, to the mobile terminal apparatus. The setting of .beta.
may be fixed according to the cell design policy (whether to
place/not to place significance on coverage), or may be controlled
dynamically according to the condition of traffic, and, for
example, set low when the traffic is light or set high when the
traffic is heavy. Also, the radio base station apparatus reports
the value of the number of users to multiplex N.sub.UE to the
mobile terminal apparatus, separately, through L1/L2 signaling, via
the PDCCH.
[0043] Then, the radio base station apparatus performs MU-MIMO
scheduling according to the reception quality of the mobile
terminal apparatus, and, depending on the scheduling result, adds
to UL grant scheduling information. In this case, an N.sub.UE field
needs to be added to UL grant.
[0044] FIG. 9 is a flowchart for explaining the transmission power
control of the second method according to the present invention.
First, a radio base station apparatus (BS) sets the attenuation
coefficient .beta. according to the cell design policy, the
condition of traffic, and so on, and reports this attenuation
coefficient .beta. to the mobile terminal apparatus (UE) (ST21).
Following this, the radio base station apparatus performs
scheduling adaptively, in TTI units, and sets the number of MU-MIMO
multiplexing N.sub.UE (ST22). Then, the radio base station
apparatus reports the number of MU-MIMO multiplexing N.sub.UE to
the mobile terminal apparatus, through L1/L2 signaling (ST23). In
this case, the transmission power information is the attenuation
coefficient .beta. and the number of MU-MIMO multiplexing
N.sub.UE.
[0045] The mobile terminal apparatus receives the attenuation
coefficient .beta. and the number of MU-MIMO multiplexing N.sub.UE,
sets transmission power according to the attenuation coefficient
.beta. and the number of MU-MIMO multiplexing N.sub.UE (ST24), and
performs uplink data transmission by the set transmission power
(ST25).
[0046] FIG. 10 is a diagram showing a configuration of a radio
communication system having a radio base station apparatus and a
mobile terminal apparatus according to an embodiment of the present
invention.
[0047] The radio communication system is a system to adopt, for
example, E-UTRA (Evolved UTRA and UTRAN). The radio communication
system has a radio base station apparatus (eNB: eNodeB) 200
(200.sub.1, 200.sub.2 . . . 200.sub.1, where 1 is an integer of
1>0), and a plurality of mobile terminal apparatuses (UEs) 100n
(100.sub.1, 100.sub.2, 100.sub.3, . . . 100.sub.n, where n is an
integer of n>0) that communicate with the radio base station
apparatus 200. The radio base station apparatus 200 is communicated
with a higher station, which is, for example, an access gateway
apparatus 300, and the access gateway apparatus 300 is connected
with a core network 400. The mobile terminal apparatus 100.sub.n
communicates with a radio base station apparatus 200 in a cell 50
(50.sub.1, 50.sub.2) by E-UTRA. Although two cells are shown with
the present embodiment, the present invention is equally applicable
to three or more cells as well. The mobile terminal apparatuses
(100.sub.1, 100.sub.2, 100.sub.3, . . . 100.sub.n) have the same
configuration, functions and state, so that the following
descriptions will be given with respect to "mobile terminal
apparatus 100.sub.n," unless specified otherwise.
[0048] In the mobile communication system, as radio access schemes,
OFDM (Orthogonal Frequency Division Multiple Access) is applied to
the downlink, and SC-FDMA (Single-Carrier Frequency-Division
Multiple Access) is applied to the uplink. OFDM is a multi-carrier
transmission scheme to perform communication by dividing a
frequency band into a plurality of narrow frequency bands
(subcarriers) and mapping data to each subcarrier. SC-FDMA is a
single carrier transmission scheme to reduce interference between
mobile terminal apparatuses by dividing, the frequency band per
terminal and allowing a plurality of terminals to use mutually
different bands.
[0049] Now, the communication channels in E-UTRA will be described.
On the downlink, the physical downlink shared channel (PDSCH),
which is used by each mobile terminal apparatus 100n on a shared
basis, and the physical downlink control channel (PDCCH) are used.
The physical downlink control channel is also referred to as the
downlink L1/L2 control channel. By this physical downlink shared
channel, user data, that is to say, normal data signal, is
transmitted. Also, by the physical downlink control channel,
downlink scheduling information (DL scheduling information),
delivery confirmation information (ACK/NACK), uplink scheduling
grant (UL scheduling grant or UL grant), and TPC command
(Transmission Power Control Command), and so on are transmitted.
The downlink scheduling information includes, for example, the ID
of a user communicating using the physical downlink shared channel,
information about that user's data transport format (that is, data
size, modulation scheme, information related to retransmission
control (HARQ: Hybrid ARQ)), downlink resource block assignment
information, and so on.
[0050] Furthermore, the above uplink scheduling grant includes, for
example, the ID of a user communicating using the physical uplink
shared channel, information about that user's data transport format
(that is, data size, information about the modulation scheme, and
so on), uplink resource block assignment information, information
about the transmission power of the uplink shared channel, and so
on. Here, an uplink resource block is equivalent to a frequency
resource and may also be referred to as a resource unit.
[0051] Also, the delivery confirmation information (ACK/NACK)
includes delivery confirmation information related to the uplink
shared channel. The content of the delivery confirmation
information is represented by either positive acknowledgment (ACK),
which indicates a transmission signal has been received properly,
or a negative acknowledgment (NACK), which indicates that a
transmission signal has not been received properly.
[0052] On the uplink, a physical uplink shared channel (PUSCH),
which is used by each mobile terminal apparatus 100n on a shared
basis, and a physical uplink control channel (PUCCH) are used. By
means of the above physical uplink shared channel, user data, that
is to say, normal data signal, is transmitted. Also, by means of
the physical uplink control channel, downlink quality information
(CQI: Channel Quality Indicator) for use in the scheduling process
for the shared physical channel on the downlink, adaptive
modulation/demodulation and coding process (AMC: Adaptive
Modulation and Coding scheme), and physical downlink shared channel
delivery confirmation information, are transmitted.
[0053] In the physical uplink control channel, in addition to the
CQI and delivery confirmation information, a scheduling request to
request uplink shared channel resource allocation, a release
request in persistent scheduling, and so on are transmitted. Here,
uplink shared channel resource allocation means that the radio base
station apparatus reports, using the physical downlink control
channel of a given subframe, to the mobile terminal apparatus, that
the mobile terminal apparatus may communicate using the uplink
shared channel in a subsequent sub frame.
[0054] The mobile terminal apparatus 100.sub.n communicates with an
optimal radio base station apparatus. In the example shown in FIG.
10, mobile terminal apparatuses 100.sub.1 and 100.sub.2 communicate
with a radio base station apparatus 200.sub.1, and a mobile
terminal apparatus 100.sub.3 communicates with a radio base station
apparatus 200.sub.2. Then, as described earlier, uplink
transmission by the mobile terminal apparatuses 100.sub.1 and
100.sub.2 becomes interference against the radio base station
apparatus 200.sub.2, which is a surrounding cell. This
surrounding-cell interference fluctuates significantly, because the
mobile terminal apparatus to be subject to transmission allocation
changes per TTI and per RB by uplink packet scheduling.
Consequently, with the present invention, the radio base station
apparatus 200.sub.2 performs fractional transmission power control,
by the above first method or second method, taking into account the
number of MU-MIMO multiplexed users, and reduces the fluctuation of
received power at the radio base station apparatus per 1 RB and 1
TTI, prevents the surrounding-cell interference from increasing,
and prevent the surrounding-cell interference from fluctuating
significantly over time in adaptive resource control. As a result
of this, it is possible to secure coverage without deteriorating
the uplink reception quality of cell-edge users.
Embodiment 1
[0055] A case will be described with the present embodiment where
fractional transmission power control is performed by the first
method. FIG. 11 is a block diagram showing a schematic
configuration of a radio base station apparatus according to an
embodiment of the present invention. The radio base station
apparatus 200 shown in FIG. 11 is mainly formed with an antenna
202, an amplifying section 204, a transmission/reception section
206, a baseband signal processing section 208, a call processing
section 210, and a transmission path interface 212.
[0056] With the radio base station apparatus 200 configured in this
way, regarding uplink data, a radio frequency signal that is
received in the antenna 202 is amplified in the amplifying section
204 to correct the received power to fixed power under AGC (Auto
Gain Control). The amplified radio frequency signal is subjected to
frequency conversion into a baseband signal, in the
transmission/reception section 206. This baseband signal is
subjected to predetermined processes (error correction, decoding,
and so on) in the baseband signal processing section 208, and
transferred to an access gateway apparatus (not shown) via the
transmission path interface 212. The access gateway apparatus is
connected to the core network, and manages the mobile terminal
apparatuses. Also, regarding the uplink, based on the uplink
baseband signal, the received SINR and interference level of a
radio frequency signal that is received in the radio base station
apparatus 200 are measured.
[0057] The call processing section 210 transmits and receives a
call process control signal to and from a radio control station of
a higher apparatus, manages the state of the radio base station
apparatus 200, and allocates resources. Note that the processes in
the layer 1 processing section 2081 and MAC (Medium Access Control)
processing section 2082, which will be described later, are
performed based on the state of communication between the radio
base station apparatus 200 and the mobile station apparatus 100 set
in the call processing section 210.
[0058] Downlink data is input in the baseband signal processing
section 208, from a higher station, via the transmission path
interface 212. In the baseband signal processing section 208, the
retransmission control process, scheduling, transport format
selection, channel coding and so on are performed, and the result
is transferred to the transmission/reception section 206. The
transmission/reception section 206 performs frequency conversion of
the baseband signal output from the baseband signal processing
section 208, into a radio frequency signal. The signal subjected to
frequency conversion is later amplified in the amplifying section
204 and transmitted from the antenna 202.
[0059] FIG. 12 is a block diagram showing a configuration of a
baseband signal processing section in the radio base station
apparatus shown in FIG. 11. The baseband signal processing section
208 is mainly formed with a layer 1 processing section 2081, a MAC
processing section 2082, an RLC (Radio Link Control) processing
section 2083, and a transmission power control section 2084.
[0060] The layer 1 processing section 2081 mainly performs
processes related to the physical layer. The layer 1 processing
section 2081, for example, performs processes for a signal that is
received on the uplink, including channel decoding, Discrete
Fourier Transform (DFT), frequency demapping, and Inverse Fast
Fourier Transform (IFFT), data demodulation and so on. Also, the
layer 1 processing section 2081 performs processes for a signal to
transmit on the downlink, including channel coding, data
modulation, frequency mapping and Inverse Fast Fourier Transform
(IFFT).
[0061] The MAC processing section 2082 performs processes for the
signal received on the uplink, such as retransmission control in
the MAC layer, scheduling for the uplink/downlink, transport format
selection for the PUSCH/PDSCH, resource block selection for the
PUSCH/PDSCH, and so on.
[0062] The RLC processing section 2083 performs, for a packet
received on the uplink/a packet to transmit on the downlink, packet
division, packet combining, retransmission control in the RLC layer
and so on.
[0063] Upon uplink MU-MIMO transmission, the transmission power
control section 2084 controls transmission power according to the
number of MU-MIMO multiplexed users.
[0064] FIG. 13 is a block diagram showing a configuration of the
transmission power control section according to embodiment 1, in
the baseband signal processing section 208 shown in FIG. 12. The
transmission power control section 2084 is mainly formed with a TPC
command processing section 20841 and a TPC command format
processing section 20842.
[0065] Upon MU-MIMO transmission, the TPC command processing
section 20841 generates a TPC command to match the number of
MU-MIMO multiplexed users, the number of fluctuating MU-MIMO
multiplexed users and so on. This TPC command is generated based on
the TPC command format selected in the TPC command format
processing section 20842 (TPC command format with an expanded
number of bits). On the other hand, in the event MU-MIMO
transmission is not involved, the TPC command defined in the LTE
system is generated. This TPC command is generated based on the TPC
command format selected in the TPC command format processing
section 20842 (TPC command format defined in the LTE system). These
TPC commands are separately reported to the mobile terminal
apparatus through L1/L2 signaling (UL grant) via the PDCCH.
[0066] The TPC command format processing section 20842 selects the
TPC command format (the Accumulate-type or the Absolute-type), and
selects the TPC command format with an expanded number of bits such
as shown in FIG. 6 or the TPC command format defined in the LTE
system. Information about this TPC command format is reported to
the mobile terminal apparatus through higher layer signaling. By
this means, transmission power information (the TPC command and the
TPC command format) to match the number of MU-MIMO multiplexed
users is transmitted from the radio base station apparatus to the
mobile terminal apparatus.
[0067] FIG. 14 is a block diagram showing a schematic configuration
of a mobile terminal apparatus according to an embodiment of the
present invention. The mobile terminal apparatus 100 shown in FIG.
14 is mainly formed with an antenna 102, an amplifying section 104,
a transmission/reception section 106, a baseband signal processing
section 108, a call processing section 110, and an application
section 112.
[0068] With the mobile terminal apparatus 100 configured in this
way, regarding downlink data, a radio frequency signal that is
received in the antenna 102 is amplified in the amplifying section
104 to correct the received power to fixed power under AGC. The
amplified radio frequency signal is subjected to frequency
conversion into a baseband signal, in the transmission/reception
section 106. This baseband signal is subjected to predetermined
processes (error correction, decoding, and so on) in the baseband
signal processing section 108, and sent to the call processing
section 110 and application section 112. The call processing
section 110 manages communication with the radio base station
apparatus 200, and the application section 112 performs processes
related to layers higher than the physical layer or the MAC
layer.
[0069] Uplink data is input in the baseband signal processing
section 108, from the application section 112. In the baseband
signal processing section 208, the retransmission control process,
scheduling, transport format selection, channel coding and so on
are performed, and the result is transferred to the
transmission/reception section 106. The transmission/reception
section 206 performs frequency conversion of the baseband signal
output from the baseband signal processing section 108, into a
radio frequency signal. The signal subjected to frequency
conversion is later amplified in the amplifying section 104 and
transmitted from the antenna 102.
[0070] FIG. 15 is a block diagram showing a configuration of a
baseband signal processing section according to embodiment 1 of the
mobile terminal apparatus shown in FIG. 14. The baseband signal
processing section 108 is mainly formed with a layer 1 processing
section 108, a MAC processing section 1082, a RLC processing
section 1083, a transmission power setting section 1084, a TPC
command receiving processing section 1085, and a TPC command format
receiving processing section 1086.
[0071] The layer 1 processing section 1081 mainly performs
processes related to the physical layer. The layer 1 processing
section 1081, for example, performs processes for a signal that is
received on the uplink, including channel decoding, Discrete
Fourier Transform, frequency demapping, Inverse Fast Fourier
Transform, data demodulation and so on. Also, the layer 1
processing section 1081 performs processes for a signal to transmit
on the uplink, including channel coding, data modulation, frequency
mapping and Inverse Fast Fourier Transform (IFFT).
[0072] The MAC processing section 1082 performs retransmission
control in the MAC layer (HARQ), analysis of downlink scheduling
information (specifying the PDSCH transport format, specifying the
PDSCH resource blocks, and so on) and so on, for a signal received
on the downlink. Also, the MAC processing section 1082 performs MAC
retransmission control, analysis of uplink scheduling information
(specifying the PUSCH transport format, specifying the PUSCH
resource blocks, and so on) and so on, for a signal to transmit on
the uplink.
[0073] The RLC processing section 1083 performs, for a packet
received on the uplink/a packet to transmit on the downlink, packet
division, packet combining, retransmission control in the RLC layer
and so on.
[0074] The TPC command receiving processing section 1085 receives a
TPC command to match the number of MU-MIMO multiplexed users
reported from the radio base station apparatus, and determines the
content of that TPC command. The TPC command receiving processing
section 1085 determines the content of the TPC command based on the
TPC command format received in the TPC command format receiving
processing section 1086. Consequently, upon uplink MU-MIMO
transmission, the TPC command receiving processing section 1085
determines the content of the TPC command based on the TPC command
format (FIG. 6) with an expanded number of bits (for example, 3
bits). Also, in the event uplink MU-MIMO transmission is not
involved, the TPC command receiving processing section 1085
determines the content of the TPC command based on the TPC command
format defined in the LTE system (2 bits). Information of the TPC
command is set to the transmission power setting section 1084.
[0075] The TPC command format receiving processing section 1086
receives a signal of the TPC command format, reported from the
radio base station apparatus. Consequently, upon uplink MU-MIMO
transmission, the TPC command format receiving processing section
1086 receives a signal of the TPC command format (FIG. 6) of an
expanded number of bits (for example, 3 bits). Also, in the event
uplink MU-MIMO transmission is not involved, the TPC command format
receiving processing section 1086 receives a signal of the TPC
command format defined in the LTE system. Information of the TPC
command format is sent to the transmission power setting section
1084.
[0076] The transmission power setting section 1084 sets
transmission power using the transmission power control information
(TPC command format and TPC command). That is to say, upon uplink
MU-MIMO transmission, transmission power is set using the TPC
command format (FIG. 6) of an expanded number of bits (for example,
3 bits) and TPC command. Also, in the event uplink MU-MIMO
transmission is not involved, the transmission power setting
section 1084 sets transmission power using the TPC command format
and TPC command defined in the LTE system.
[0077] In this radio communication system, a radio base station
apparatus, which performs space division multiplexing between users
by multi-user MIMO transmission, controls transmission power
according to the number of MU-MIMO multiplexed users, and transmits
transmission power information to match the number of MU-MIMO
multiplexed users, and a mobile terminal apparatus sets
transmission power using transmission power information and
transmits an uplink signal by that transmission power.
[0078] That is to say, upon MU-MIMO transmission, the radio base
station apparatus selects the TPC command format (the format with
an expanded number of bits), and reports the selected TPC command
format to a mobile terminal apparatus to which MU-MIMO transmission
is anticipated to be applied, through higher layer signaling. Then,
together, whether the TPC command is the Accumulate-type or the
Absolute-type is also reported. Following this, the radio base
station apparatus performs scheduling adaptively in TTI units,
determine the TPC command in the selected TPC command format, and
reports the TPC command to the mobile terminal apparatus to be
scheduled, by L1/L2 signaling.
[0079] In the mobile terminal apparatus, a TPC command to match the
number of fluctuating MU-MIMO multiplexing or the number of MU-MIMO
multiplexing is reported from the radio base station apparatus. The
mobile terminal apparatus sets transmission power according to the
reported TPC command, and performs uplink data transmission by the
set transmission power.
Embodiment 2
[0080] A case will be described with the present embodiment where
fractional transmission power control is performed by the second
method. FIG. 16 is a block diagram showing configuration of
transmission power control section according to embodiment 2 of
baseband signal processing section 208 shown in FIG. 12. Note that
the configurations of the radio base station apparatus shown in
FIG. 11 and FIG. 12 are the same as in embodiment 1 and will not be
described in detail.
[0081] The transmission power control section 2084 is mainly formed
with a .beta. processing section 20843 and a N.sub.UE setting
section 20844.
[0082] The .beta. processing section 20843 generates attenuation
coefficient .beta.(0.ltoreq..beta..ltoreq.1). This attenuation
coefficient .beta. is set as appropriate taking into account the
relationship between capacity and coverage. In the event MU-MIMO
transmission is applied, if significance is placed on coverage,
.beta.=1 is set. In the event MU-MIMO transmission is not applied,
.beta.=0 is set (fractional transmission power control in the LTE
system). The attenuation coefficient .beta. may be reported via the
PBCH or may be reported separately through higher layer
signaling.
[0083] The N.sub.UE processing section 20844 performs scheduling
according to the reception quality of the mobile terminal
apparatus, in the same way as by the MAC processing section 2082,
and sets the number of MU-MIMO multiplexing N.sub.UE. The value of
the number of MU-MIMO multiplexing N.sub.UE is reported separately
by L1/L2 signaling, via the PDCCH.
[0084] FIG. 17 is a block diagram showing a configuration of a
baseband signal processing section according to embodiment 2, in
the mobile terminal apparatus shown in FIG. 14. Components in FIG.
17 that are the same as in FIG. 14 will be assigned the same codes
as in FIG. 14 and their detailed descriptions will be omitted. The
baseband signal processing section 108 is mainly formed with a
layer 1 processing section 1081, a MAC processing section 1082, an
RLC processing section 1083, a transmission power setting section
1084, a .beta. receiving processing section 1087, and an N.sub.UE
receiving processing section 1088.
[0085] Upon uplink MU-MIMO transmission, the .beta. receiving
processing section 1087 receives an attenuation coefficient .beta.
reported from the radio base station apparatus, and determines its
content. Information about the attenuation coefficient .beta. is
sent to the transmission power setting section 1084.
[0086] Upon uplink MU-MIMO transmission, the N.sub.UE receiving
processing section 1088 receives a signal of the number of MU-MIMO
multiplexing N.sub.UE that is reported from the radio base station
apparatus, and determines its content.
[0087] Information about the number of MU-MIMO multiplexing
N.sub.UE is sent to the transmission power setting section
1084.
[0088] The transmission power setting section 1084 sets
transmission power using transmission power control information
(the attenuation coefficient .beta. and the number of MU-MIMO
multiplexing N.sub.UE). That is to say, upon uplink MU-MIMO
transmission, transmission power is set, according to above
equation 2, using the attenuation coefficient .beta. and the number
of MU-MIMO multiplexing N.sub.UE. Also, the transmission power
setting section 1084 sets transmission power according to above
equation 1 in the event uplink MU-MIMO transmission is not
involved.
[0089] In this radio communication system, a radio base station
apparatus, which performs space division multiplexing between users
by multi-user MIMO transmission, controls transmission power
according to the number of MU-MIMO multiplexed users, and transmits
transmission power information to match the number of MU-MIMO
multiplexed users, and a mobile terminal apparatus sets
transmission power using transmission power information and
transmits an uplink signal by that transmission power.
[0090] That is to say, upon MU-MIMO transmission, the radio base
station apparatus sets the attenuation coefficient .beta. according
to the cell design policy, traffic conditions, and so on, and
broadcasts this attenuation coefficient .beta. to the mobile
terminal apparatus (UE). Next, the radio base station apparatus
performs scheduling adaptively in TTI units, and sets the number of
MU-MIMO multiplexing N.sub.UE. Then, the radio base station
apparatus reports the number of MU-MIMO multiplexing N.sub.UE to
the mobile terminal apparatus through L1/L2 signaling.
[0091] The mobile terminal apparatus receives the attenuation
coefficient .beta. and the number of MU-MIMO multiplexing N.sub.UE,
sets transmission power according to the attenuation coefficient
.beta. and the number of MU-MIMO multiplexing N.sub.UE, and
performs uplink data transmission by that set transmission
power.
[0092] Also, the embodiments disclosed herein are only examples in
all respects, and are by no means limited to these embodiments. The
scope of the present invention is defined not only by the
descriptions of the above embodiments and also is set by the
claims, and covers all the modifications and alterations within the
meaning and range equivalent to the claims.
INDUSTRIAL APPLICABILITY
[0093] The present invention is suitable for use for a radio base
station apparatus and a transmission power control method in the
LTE system.
[0094] The disclosure of Japanese Patent Application No.
2010-087266, filed on Apr. 5, 2010, including the specification,
drawings, and abstract, is incorporated herein by reference in its
entirety.
* * * * *